Mar 22, 2013 / Water conservation

So only .75% of all the water on earth is usable by humans and that water is caught up somewhere in what we call The Water Cycle.

You can study the above diagram, taken from the USGS web site, and follow the path of water as it travels through the water cycle.  Most of the terms are common and self explanatory.

There are two terms above that I was not sure of when I first saw this diagram:


According to the Salinity Management Guide, “evapotranspiration is the sum of evaporation from the land surface plus transpiration from plants. Precipitation is the source of all water.”

The other term that flummoxed me was


The USGS defines sublimation as sublimation as “the conversion between the solid and the gaseous phases of matter, with no intermediate liquid stage. For those of us interested in the water cycle, sublimation is most often used to describe the process of snow and ice changing into water vapor in the air without first melting into water. The opposite of sublimation is ‘deposition’, where water vapor changes directly into ice—such a snowflakes and frost.”

So, ALL of the usable water is caught up somewhere in the water cycle. But, not all of it is actually available for use at any one moment. Some water is in snow and ice, some in clouds, some in soil moisture, some in ground ice and permafrost, and….well you get the idea.

Green Plumbers™ USA estimates that 0.25%-0.30% of USABLE water is actually available at any one moment for human use. Of course, this is an estimate.

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